Conventional micropropagation to produce differentiated plant biomass is generally expensive and labor intensive. Various types of vessels have therefore been developed for in vitro culture of plants so as to overcome these issues. The methodologies used in these vessels can be divided roughly into four types: liquid-phase, gas-phase, hybrid bioreactors and temporary immersion systems (TIS).
A temporary immersion system is a periodic, semi-automated or fully automated cultivation system based on alternating cycles of temporary immersion of the cultured plant tissue into a liquid medium followed by draining and exposing the plant tissue to a gaseous environment. Usually the immersion period is relatively short, in the region of a few minutes, whereas the air exposure period is prolonged, in the region of several hours. By adjusting the duration of periods of immersion and exposure it is possible to create conditions for optimal humidity and supply nutrients with minimal liquid contact, thereby making it possible to reduce significantly the hyperhydricity of the cultured plant tissue.
As well as reducing hyperhydricity of the cultured plant tissue, temporary immersion systems are considered the best for the production of differentiated plant tissue because they produce more plants per square meter. They have higher multiplication rates and the use of a liquid medium reduces agar costs. Temporary immersion results in higher nutrient uptake and assimilation, and forced aeration increases growth and biomass production. Reduced manipulations and reduced labor costs are another advantage, together with improved plant quality and the production of higher fresh and dry weight yields.